They are able to project the results. If they were able to say Romney lost Ohio early on Election night in 2012, then after a couple of days they could have said MI was Trump or PA by midnight.
Of course they can project results. Romney was projected to lose because the vote count still uncounted was in Obama areas.
The same was true this time. Trump had a big rural lead, that got smaller and smaller, and the unknowns about absentee counts and perhaps even more profoundly the provisional counts left room for doubt.
I watched the Wisconsin recount carefully and the absentee issue is pretty big, especially in big counties. It’s always going to be like this, and it doesn’t have to mean anyone is cheating. The big counties take longer, and have more uncertainty as to absentee counts, for the networks to endure.